# std::future_error

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< cpp‎ | thread

Defined in header `<future>` |  |
class future_error; |  | (since C++11)

The class std::future_error defines an exception object that is thrown on failure by the functions in the thread library that deal with asynchronous execution and shared states (std::future, std::promise, etc). Similar to std::system_error, this exception carries an error code compatible with std::error_code.

Inheritance diagram

### Member functions

(constructor) | creates a `std::future_error` object (public member function)
operator= | replaces the `std::future_error` object (public member function)
code | returns the error code (public member function)
what | returns the explanatory string specific to the error code (public member function)

## Inherited from std::logic_error

## Inherited from std::exception

### Member functions

(destructor) [virtual] | destroys the exception object (virtual public member function of `std::exception`)
what [virtual] | returns an explanatory string (virtual public member function of `std::exception`)

### Example

Run this code

    #include <future>
    #include <iostream>

    int main()
    {
        std::future<int> empty;
        try
        {
            int n = empty.get(); // The behavior is undefined, but
                                 // some implementations throw std::future_error
        }
        catch (const std::future_error& e)
        {
            std::cout << "Caught a future_error with code \"" << e.code()
                      << "\"\nMessage: \"" << e.what() << "\"\n";
        }
    }

Possible output:

    Caught a future_error with code "future:3"
    Message: "No associated state"

### See also

future_errc (C++11) | identifies the future error codes (enum)

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